The present invention is directed to a production line framing system for accurately locating major panels of a unitized automobile body relative to each other for the initial welding of these panels into their permanently assembled relationship to each other.
The construction of a so called unitized automobile body commences with the formation of individual major panels by stamping the panels from a sheet metal blank. Typically, these major panels include a floor panel, right and left body side panels, a fire wall and either a roof panel or transversely extending header members upon which a roof panel is subsequently mounted. After the individual panels are stamped, some preliminary assembly operations may be performed on the individual panels as, for example, adding door hinge and latch hardware to the body side panels at appropriate locations on the door opening, adding seat mounting brackets and reinforcements to the floor panel, etc.
A set of panels which are to constitute a subassembly of the finished vehicle body are then brought together and loosely assembled to each other. This initial loose assembly frequently is accomplished by a so called toy tab arrangement in which one panel is formed with a tab projecting from one edge which is received in a slot in an adjacent panel. This technique interlocks the panels and frame members to each other to the point where they will not separate from each other, but does not achieve a rigid assembly--that is, for example, the side panels may tilt slightly relative to the floor panel. The loosely assembled subassembly is then brought to a welding station which welds the various panels and frame members to each other into a rigid permanently assembled relationship.
This initial welding step is one of the most important steps in the assembly of the body because it establishes the final assembled alignment of the various panels and headers to each other and an accurate and precise alignment is essential to further assembly steps performed on the subassembly by automated tooling at subsequent stations along the production line. It is thus essential that the various panels and headers by precisely and accurately located relative to one another and held fixedly in the desired positions during the welding operation. The positioning of the various panels and header members during the welding operation is accomplished by clamping frames which carry a plurality of individual clamps arranged to clamp the various body components in the desired position.
Most present day body framing lines employ robotic welders which can be programmed to perform several welds at different locations on the body during one welding operation. The welders typically are located at opposite sides of the conveying line at the welding station, and when the body subassembly is located at the welding station, the head of one welder may, for example, be extended to pass through the door opening to apply several tack welds along the seam between a body side panel and floor panel. In those cases where the clamping frames are positioned at opposite sides of the body, see, for example, DeCandia U.S. Pat. No. 4,162,387, clearance problems may restrict motion of the welding head which must past through the clamping frame before it has access to the body. This can require the performance of a portion only of the required welding at one station and the advancement of the partially welded subassembly to a second station where a different clamping frame provides access of the welding head to portions of the assembly which could not be reached by the heads at the first station.
A second problem which arises where separate clamping frames are employed at opposite sides of the body is that the two frames must be independently located in a predetermined relationship to each other and to the position occupied by the body which the frames are to clamp.
In U.S. Pat. No. 4,670,961, front and rear clamping frames are carried by rotary magazines into positions above the front and rear portions of a vehicle body and are then lowered into an operating position in overlying relationship to the body to clamp the various panels. This arrangement reduces the clearance problem discussed above. However, like the system referred to above in which two independent clamping frames were respectively employed at the opposite sides of the vehicle body, the system of U.S. Pat. No. 4,670,961 likewise requires that two separate frames be independently located relative to the body and to each other.
The present invention is directed to a clamping system which, when located in operative relationship with the vehicle body, overlies the body to leave the sides of the body free of obstructions to movement of the welding heads, and which requires the alignment of only a single frame assembly with the body.